Wastewater Treatment

Elk River Wastewater Treatment Plant

Photo of Waste Water Treatment Plant


The mission of the Elk River Wastewater Treatment Plant is to protect public health, the environment, and to provide for the beneficial use of the waters in the greater Eureka area. Beneficial uses include all commercial and recreational activity as well as protection of the natural wildlife habitat found in the area.

The Elk River Wastewater Treatment Plant was commissioned in June of 1984. It is located on the East side of Humboldt Bay near the mouth of the Elk River. In addition to the area encompassing the process structures and equipment, the plant maintains 139 acres of dedicated wildlife wetlands. The wetlands are comprised of freshwater and tidal marshes, ponds, and riparian habitats.

The plant serves customers within the City of Eureka and also treats wastewater from the surrounding unincorporated areas served by the Humboldt Community Services District. The total population served by the plant is approximately 45,000.


The Elk River Wastewater Treatment Plant incorporates the trickling filter/solids contact process to achieve secondary treatment standards. Treated wastewater is retained in the effluent holding pond until an ebb tide occurs in Humboldt Bay. On ebb tides, the effluent is dechlorinated and discharged to the main channel of the bay. The outgoing tide carries the treated wastewater past the mouth of Humboldt Bay and into the ocean. This ebb tide discharge provides the functional equivalent of an ocean outfall and virtually eliminates the possibility of the discharge impacting the shellfish harvesting areas located in North Bay. Wastewater solids are anaerobically digested and then stored in facultative sludge lagoons for up to two years. During the summer months, the stabilized biosolids are dredged from the lagoons and land applied at an agronomic rate as a soil conditioner at the City-owned biosolids reclamation site. The reclamation site has been utilized as a pasture for grazing beef cattle and is currently used to cultivate grass hay that is cut and baled several times a year.